IDW said they won't be introducing any new characters in year 2 (issues 13-24), so I wouldn't expect anyone until 2020 at least. Even then, its more likely to be game characters who haven't been introduced to the comics yet (ie, Big). They've got plenty to work with already- Whisper and Tangle need panel time, as do Rough and Tumble, even most of the games cast has gotten one issue each thus far, the current setting/continuity needs to be developed, Silver and Blaze's worlds, Eggman's return to form, etc. I think there's plenty to get through before expanding the cast even more.
Now that its been mentioned, I think a lot of recurring female heroes were lost with the Archie continuity- Sally and Bunnie in particular, Nicole, Honey, etc. just off the top of my head. That kinda just leaves the cast with Amy, Rouge (who's basically tied to Shadow), Blaze (who's from another world and rarely gets to appear), and Cream (who's notoriously difficult to write in an action setting), so it makes sense that Tangle and Whisper were introduced to be recurring characters.